In an attempt to thwart spammers, Google Mail has started using mobile phone numbers to provide customers with gmail invitations. This is an interesting development, one that has been predicted for at least since the miniaturizaion of mobile telephones. With number portability in the United States, this finally becomes a possibility for many corporations.
Mobile numbers stay with you. Although they can be stolen and are notoriously insecure devices, they do offer some relative assurance that you are the individual you claim to be. It beats having to ask for people’s Social Security Number or Carte d’Identite for lower security items where you need to insure that this is one person rather than many. For anti-spam abuse, it makes remarkable sense: it is much, much more difficult and expensive to acquire a mobile number than it is to acquire an email address.
Look for your mobile phone to be increasingly used for identity purposes. Expect that your phone will soon come with better security controls, probably biometric based. Yes, it will be yet another thing to fall apart, but it does increase security without you having to divulge something that isn’t already widely known.